Panes of glass, especially those of motor vehicles, are often provided with a pane surround or a frame made of plastic which has a certain cross-sectional profile, by means of which the pane is inserted and fixed in a predetermined opening, e.g., an opening in the body. In general, the pane surround or frame also serves at the same time to seal off the pane relative to the adjoining component.
Some pane surrounds of this kind are molded directly on the pane by injection molding after the prior application to the pane of an adhesion promoter to achieve better bonding of the pane of glass to the plastic of the pane surround. This molding-on process takes place in a rigid injection mold in which the pane is accommodated. There are cavities in the interior of the injection mold where the plastic is intended to form the pane surround. The plastic is forced into the injection mold at high pressure to ensure that it reliably fills the cross-sectional profile in all its ramifications.
Such injection molds are of very complicated construction and accordingly are very expensive. For various reasons, these injection molds are subjected to severe wear, making it necessary repeatedly to overhaul at least individual parts and sometimes even the entire mold or to replace the entire mold. This gives rise to further costs for the mold.
The injection mold is composed of steel. For this reason, it is inflexible in relation to the pane of glass. The panes of glass themselves are produced by a thermoforming process because they are often curved in three dimensions. Because of the properties of the glass and the production process for the panes, the panes have considerably higher tolerances as regards their dimensions and their dimensional accuracy than the steel injection mold. If the pane is oversized, particularly as regards to its thickness or in the case of deviations from its nominal shape, the pane is broken either while being clamped in the mold or during the subsequent injection of the plastic. As crumbs of glass, the fragments can have very small dimensions, making it difficult to remove them completely from the injection mold before the next pane is inserted. The very small fragments, in particular, lead to damage to the surface of the injection mold or even to damage of the next pane. However, they can also lead to defects in the pane surround. If the pane is undersized, particularly as regards to its thickness, it is to be expected that the plastic will in part escape through the gap then present between the injection mold and the pane and that outgrowths or "flash" will form. This must be removed subsequently by hand whenever it is visible and impairs the appearance of the pane and its surround. This finishing of the panes is very time-consuming, requires careful workers and is accordingly expensive. Moreover, there is also the danger here that the pane of glass and/or its surround will be damaged during the removal of the outgrowths of material by the tools used for removal and that the essentially finished pane will therefore subsequently turn into scrap.